The foam or head that is normally present in a glass of beer is an important feature of the product, and it has been found that many consumers, when judging the quality of a beer, consider that this is one of the more important factors. Much the same is also true of other beverages on which a head is formed. A foam head is of good quality if it has a number of attributes, among which are stability, the ability to form lacing (that is a lace like pattern of bubbles that is left on the side of the glass after the liquid beer or other beverage has been wholly or largely consumed), good color (usually white) and a preponderance of small substantially uniform sized bubbles.
The nature of the foam head on a glass of beer or other beverage depends principally on two factors, one being the constitution or composition of the beverage itself and the other being the way in which the beverage is dispensed. At least inasfar as its application to beer is concerned, the present invention is primarily concerned with the former of these two factors.
A typical brewing process yields beer with a significant content of unassimilated proteins, and, even though most of these proteins originate from malt, some are derived from hops and from the yeast culture used. Certain of such proteins present in beer have been implicated in foam stabilization, such as cystine-poor proteoses, while others (eg albumins, barley hordeins, cystine-rich proteoses) are known to contribute to undesirable haze formation in beer. To some degree, beer haze can be dealt with through the use of various purely physical methods such as filtration or centrifugation. The drawbacks of clarifying beer using only such methods are well known, particularly in association with beverages in which the precipitable proteins are present in solution, and above all if they are of widely differing molecular weights in which case filtration can be extremely difficult and centrifugation of limited value. Moreover, this limited clarification does little, if anything to secure against recurrent haze formation on subsequent storage.
Reversible haze formation in beer, for example, results when even carefully filtered beer is stored at lower temperatures, and is referred to as chill haze formation. Various and diverse approaches exist for dealing with this aspect of the haze problem, and these come under the broad category of chillproofing the beverage.
The above mentioned physical methods are sometimes augmented through the use of adsorbent materials. By way of example, it is known that silica adsorbents or silica hydrogels added to beer adsorb offending proteins which can be removed during primary and/or secondary filtration of the beer. Another example of the use of adsorbents involves contacting the beer with polyvinylpolypyrrolidone to remove the polyphenols that are indigenous to beer and that are believed to participate in the protein condensation reactions that result in chill haze formation.
Conventional chillproofing processes more commonly involve the addition of an enzyme preparation to the beer and especially ales, either alone or in combination with one or more of the above mentioned processes. Enzymatic hydrolysis as applied to the chill haze problem, produces the desired two fold effects of: eliminating or at least substantially reducing the permanent haze and thereby faciliting subsequent filtration or centrifugation steps; and, acting on dissolved or colloidal macromolecules, degrading the proteinaceous components into small peptides, thereby increasing their solubility and impeding subsequent precipitation reactions and thus reducing or even eliminating latent haze formation, especially chill haze formation. Known enzymatic systems which are used for chillproofing include papain, bromelain, ficin, pepsin, and certain microbial proteases.
The most commonly used commercial enzymes are of plant origin and are known to have been used in brewing since almost the beginning of the century. In spite of some well known shortcomings, these products continue to be used even today, and despite the availability of a number of microbial enzymes as alternatives. Current commercial practices therefore include the use of solutions rich in papain derived from Carica papaya (papaya), or rich in ficin derived from the latex of Fiscus glabrata (fig). Other vegetable materials less commonly used as a source of chill haze treating enzymes include mushrooms and barley.
There are, however, a variety of microbial enzymes known to have application in dealing with the chill haze problems associated with beer. U.S. Pat. No. 4,038,419, for example, relates to the use of a microbial protease derived from Streptomyces, which is auto destructive, can be sterilized using dry heat, is active over a wide range of pH, and is effective in the same way as the papain and other vegetable protease mentioned hereinabove.
U.S. Pat. No. 3,712,820; 3,795,745; and 3,711,292 also teach the use of various neutral and alkaline proteases in connection with the production of beer. These patents are particularly concerned with the use of these enzymes to enhance the release of yeast nutrients from barley without having to rely on the addition of malt, or at least without having to rely on the addition of as much malt as is required in the production of more conventional products. Concomitant benefits associated with chill haze improvements are also noted. Although these three patents suggest that the other properties of the beer are not adversely effected by way of this treatment of the beer, the foam SIGMA values reported in the examples are consistently lower than untreated control beers, and in some cases sufficiently so as to suggest a significant reduction in foam stability as a result of the treatments in question.
U.S. Pat. No. 3,740,233, also makes that point that commercial chillproofing enzymes, and in particular the use of papain, resulted in a marked deterioration of foam stability in treated beers. This patent notes that in addition to producing improved stability against chill haze formation, such treatments must not adversely affect the quality of finished beers, particularly as regards their flavour and foam stability. According to this same patent, the foam stability can be preserved notwithstanding the chill haze treatment when acidic protease enzymes derived from Mucor pusillus Lindt are added to the fermenter in combination with a second enzyme treatment using either the same Mucor enzymes or commercial chill haze (papain) enzymes added to primary filtered beer.
A seemingly similar type of approach is taken in U.S. Pat. No. 4,181,742 which teaches that the addition of chill proofing enzymes results in the production of beverages which have a tendency to gush when opened. According to the disclosure of this patent, this can be overcome through the use of a pepsin inhibitor to inhibit a microbial acidic protease that is used in conjuction with conventional chill proofing enzymes that are employed to control chill haze in known manner. The inhibition of the proteolytic action is taught as essential to this purpose. In this regard it is known in the art that the presence of active microbial acid proteases in beer can prejudice foam stability, as pointed out in Nielsen, H. et al, Brauwelt International, 1988, "Damage to beer foam by enzymes from yeast", and earlier works cited in that article, by Maddox et al, Proc. EBC, 1955, S. 315 and Biochem. J. 117, 843, 1970.
CRC Critical Reviews in Biotechnology, volume 8, issue 2, 1988, in an article entitled "APPLICATION OF EXTRACELLULAR YEAST PROTEASES IN BEER STABILIZATION" and an earlier article entitled "APPLICABILITY OF YEAST EXTRACELLULAR PROTEINASES IN BREWING: PHYSIOLOGICAL AND BIOCHEMICAL ASPECTS" Applied Environmental Microbiology, volume 53, number 3, 1987, both teach that a combination of concentrated wort proteins and an extracellular protease produced by Torulopsis sp., result in improvements in chill haze control, without detrimental effects to the foam stability of the resulting beer. The later of these two articles contains data showing that the foam stability is directly attributable to the presence of the concentrated wort proteins. The use of various proteins is known for this purpose, as is disclosed in EU 138 341, which goes on to observe that the addition of such proteins as a rule results in increased chill haze formation in the protein supplemented product, in the absence of appropriate chillproofing enzymes. Of the proteins reported in that patent specification, only hydrolysed egg albumin could be used on its own to improve foam stability without giving rise to concomitant chill haze problems.
There remains a need for improved chill haze and foam stabilizing treatments for, inter alia, malt beverages.